Casting unit and casting method

ABSTRACT

The casting unit solves problems of a conventional casting unit, in which a non-consumable sprue is connected to a lost foam gate attached to a core, such as troublesome assembly and post-treatment after casting. In the casting unit, a plurality of cores having molten metal inlets, which open into the surfaces of the cores and through which a molten metal is caused to flow into cavities formed in the cores, and a lost foam pattern, which forms a sprue between each of the molten metal inlets and a sprue cup, in which a molten metal is poured, and which has a peripheral surface coated with a refractory mold coating agent, are embedded in dry sand except for the sprue cup, and the cores, which are adjacent to each other, are connected to each other so that the plurality of cores are integrated.

FIELD OF TECHNOLOGY

The present invention relates to a casting unit and a casting method.

BACKGROUND OF TECHNOLOGY

A conventional casting method in which a lost foam pattern composed of resin, e.g., styrene foam, is used is known.

In the above described conventional method, a casting unit shown in FIG. 17 is used. In the casting unit shown in FIG. 17, dry sand 106 is stored in a metal flask 100, and a lost foam pattern, which is composed of resin, e.g., styrene foam, and which includes product sections 102 and a sprue section 104, is embedded the dry sand, except for a sprue cup 108, which is provided to an upper end of the sprue section 104.

A tubular member 110 having a plurality of through-holes 110 a, 110 a, . . . , whose diameter is smaller than a grain diameter of the dry sand 106, is inserted in the dry sand 106 so as to collect and discharge a decomposition gas, which is generated by contact between the lost foam pattern and the molten metal.

In the conventional casting method using the casting unit shown in FIG. 17, the resin of the lost foam pattern, e.g., styrene foam, is thermally decomposed and lost by heat of a molten metal by pouring the molten metal into the sprue cup 108, so that the product sections 102 and the sprue section 104 can be filled with the molten metal.

Note that, the decomposition gas from the resin, e.g., styrene foam, is introduced into the tubular member 110, via gaps between grains of the dry sand 106, and discharged to the outside.

In the conventional casting method using the casting unit shown in FIG. 17, a plurality of cast products can be integrated, so post-treatment after casting can be easily performed. However, an ordinary lost foam pattern is produced by molding grains of resin, e.g., styrene foam, so vestiges of the grains are formed on a surface of the lost foam pattern. Therefore, the vestiges will be transferred onto surfaces of the cast products. Therefore, the surfaces of the cast products must be ground or polished.

In case that the product sections 102 are large, a part of the lost foam pattern will be left or soot will be generated. If the left part of the lost foam pattern or the soot is included in the cast products. The cast products including the left part of the lost foam pattern or the soot must be treated as bad products.

Besides the above described conventional casting method using the lost foam pattern, Patent Document 1 discloses another conventional casting method performed in a casting unit shown in FIG. 18, in which a core 202 including a cavity 202 a, a feeder head 202 b communicated to the cavity 202 a, a lost foam gate 206 composed of resin and connected to the core 202 and a non-consumable sprue section 204 are embedded in dry sand 208 stored in a metal flask 200.

In the casting unit shown in FIG. 18, a sprue cup 210 is exposed from the dry sand 208 and attached to an upper end of a non-consumable sprue section 204, and a depressurizing wire mesh pipe 212 is inserted in the dry sand 208.

Further, a film 214 for depressurization sealing covers a surface of the dry sand 208.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Laid-open Patent Publication No. P6-226422

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In case of using the casting unit shown in FIG. 18, a molten metal is poured into the sprue cup 210 in a state where an inner pressure of the flask 200 is reduced by sucking air from the depressurizing wire mesh pipe 212, then the molten metal flowing down the non-consumable sprue section 204 thermally decomposes the resin of the lost foam gate 206 and fills the cavity 202 a of the core 202.

Decomposition gasses, which are generated by thermally decomposing the resins of the lost foam gate 206 and the core 202, are discharged from the depressurizing wire mesh pipe 212 via gaps between grains of the dry sand 208.

In the casting unit shown in FIG. 18, transferring vestiges of the resin grains onto a surface of a cast product can be prevented. Further, the lost foam pattern is small, so leaving a part of the lost foam pattern and generating soot can be prevented.

However, in the casting unit shown in FIG. 18, the non-consumable sprue section 204 must be an earthenware pipe, so there are some problems, such as troublesome assembly and post-treatment after casting.

In case of using a plurality of cores, a non-consumable branch pipe or pipes are required, so the assembly and the post-treatment must be more troublesome.

An object of the present invention is to provide a casting unit and a casting method, which are capable of: solving the problems of the conventional casting units, in which the non-consumable sprue is connected to the lost foam gates of the cores, such as troublesome assembly and post-treatment after casting; preventing vestiges of resin grains from being transferred onto surfaces of cast products; preventing a part of lost foam pattern from being left in the products; preventing generation of soot; and easily performing the assembly and the post-treatment after casting.

Means for Solving the Problems

The inventors of the present invention have studied to solve the above described problems of the conventional casting units, and they found that even if the entire sprue connecting a plurality of cores, in which cavities are formed, to a sprue inlet was formed as a lost foam pattern, an amount of resin for forming the lost foam pattern could be less than that of the resin for forming the lost form pattern shown in FIG. 17 which forms the sprue section 104 and the product sections 102. Therefore, the inventors found that the resin of the lost foam pattern could be fully thermally decomposed by the molten metal poured into a sprue inlet, and a decomposition gas could be discharged to the outside via the cores and gaps between grains of dry sand.

Further, the inventors found that the plurality of cores could be treated as one body by connecting and integrating the adjacent cores, so that they reached the present invention.

To solve the above described problems, the inventors provide a casting unit comprising: a plurality of cores having molten metal inlets, which open into the surfaces of the cores and through which a molten metal is caused to flow into cavities formed in the cores; and a lost foam pattern forming a sprue between each of the molten metal inlets and a sprue inlet, in which a molten metal is poured, the lost foam pattern having a peripheral surface coated with a refractory mold coating agent, wherein the cores and the lost foam pattern are embedded in dry sand except for the sprue inlet, and wherein the cores, which are adjacent to each other, are connected to each other so that the plurality of cores are integrated.

Further, the inventors provide a casting method performed in the casting die of the present invention, comprising the steps of: plasticizing the dry sand, by applying vibration, after pouring the molten metal into the sprue inlet; and pulling a cast body, in which runners, which are formed by filling the sprue formed by the lost foam pattern with the molten metal, and products, which are formed by filling the cavities of the cores with the molten metal, are integrated, out of the dry sand.

As to the casting unit and the casting method provided by the inventors, preferable aspects will be explained.

By connecting the cores, which are adjacent to each other, to each other by an adhesive or concavo-convex engagement, the plurality of cores can be easily connected and integrated.

By constituting each of the cores by a pair of core molds, the cores in which the cavities are respectively formed can be easily produced. Preferably, the cores are constituted by shell molds, self-hardening molds or combination of the both.

In case that the cores are constituted by the shell molds, the plurality of the cores can be highly easily connected by bringing softened layers of the shell molds, in which resin included in the shell sand is softened, into tight contact with each other and hardening the softened layers.

By coating inner wall faces of the cavities formed in the cores with a refractory mold coating agent, the casting can be performed with a high temperature molten metal.

Further, the casting unit can be downsized by: inserting the cores, the sprue, the sprue inlet and the dry sand into a metal flask; and inserting a tubular member having a plurality of through-holes, whose diameter is smaller than a grain diameter of the dry sand, into the dry sand so as to collect and discharge a decomposition gas, which is generated by contact between the cores, the lost foam pattern and the molten metal.

Effects of the Invention

In the casting unit invented by the inventors, even if the sprue, which connects each of the cores in which the cavities are formed to the sprue inlet, is formed by the lost foam pattern, the resin of the lost foam pattern can be fully thermally decomposed by the molten metal poured into the sprue inlet, and the thermally-decomposed gas can be discharged to the outside via the cores and gaps between grains of the dry sand. Therefore, leaving a part of the lost foam pattern and generating soot can be prevented, so that invasion of the lost foam pattern or soot into cast products can be prevented.

The plurality of cores can be integrated by connecting the cores, which are adjacent to each other, to each other, so that the integrated cores can be treated as one body and the integrated cores can be easily handled when the casting unit is assembled.

After casting, the cast products, which are formed by filling the cavities with the molten metal, and the runners, which are formed by filling the sprue with the molten metal, are integrated as one cast body. Therefore, the cast body can be easily pulled out from the dry sand.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] is a sectional view of an embodiment of the casting unit relating to the present invention.

[FIG. 2] is a front view of cores 12 and 12 used in the casting unit shown in FIG. 1.

[FIG. 3] is a sectional view of the casting unit shown in FIG. 1, which explains the casting method using the casting unit.

[FIG. 4] is a sectional view of a cast body 30, which has been pulled out from dry sand 24 after completing the casting operation performed in the casting unit.

[FIG. 5] is a front view of the cores 12 shown in FIG. 1, in which the six cores are aligned. [FIG. 6] is a front view of another core 12, which can be used in the casting unit relating to the present invention.

[FIG. 7] is an explanation view of the cores 12 shown in FIG. 6, in which the six cores are aligned.

[FIG. 8] is an explanation view of an equipment for connecting cores which are constituted by shell molds.

[FIG. 9] is an explanation view of a first step of producing the shell molds, which are used for connecting the cores.

[FIG. 10] is an explanation view of a second step of producing the shell molds following the step shown in FIG. 9.

[FIG. 11] is an explanation view of a third step of producing the shell molds following the step shown in FIG. 10.

[FIG. 12] is an explanation view of a fourth step of producing the shell molds following the step shown in FIG. 11.

[FIG. 13] is an explanation view of a fifth step of producing the shell molds following the step shown in FIG. 12.

[FIG. 14] is an explanation view of a sixth step of producing the shell molds following the step shown in FIG. 13.

[FIG. 15] is an explanation view of a seventh step of producing the shell molds following the step shown in FIG. 14.

[FIG. 16] is an explanation view of an eighth step of producing the shell molds following the step shown in FIG. 15.

[FIG. 17] is a sectional view of the conventional casting unit using the lost foam pattern.

[FIG. 18] is a sectional view of the conventional casting unit using the core and the lost foam pattern.

EMBODIMENTS OF THE INVENTION

An embodiment of the casting unit relating to the present invention is shown in FIG. 1. In the casting unit shown in FIG. 1, two cores 12 and 12 are inserted in a metal flask 10. As shown in FIG. 2, each of the cores 12 and 12 is constituted by a pair of core molds 12 a and 12 b, which are connected to each other, and a cavity 14 is formed therein. Each of ingates 16, which acts as a molten metal inlet for introducing a molten metal into the cavity 14 of the core 12, is located in an upper slope face of the core 12 and formed on a parting line between the core molds 12 a and 12 b. The ingates 16 may be formed in optional places, other than the parting lines, according to shapes of the cores 12.

By coating inner wall faces of the cavities 14 with a refractory mold coating agent, a high temperature molten metal, e.g., molten stainless steel, can be used for casting.

Note that, the pair of core molds 12 a and 12 b may be constituted by shell molds, self-hardening molds or combination of the both.

Further, the cores 12 and 12 shown in FIGS. 1 and 2 are integrated by connecting their outer faces to each other with an adhesive, so that the cores 12 and 12 can be handled as one body.

A sprue is formed, by a lost foam pattern 20, between the ingates 16, which are respectively provided to the cores 12 and 12, and a sprue cup 18, i.e., sprue inlet, composed of ceramic. The lost foam pattern 20 is composed of resin, e.g., styrene foam. An inverted triangle part 20 a of the lost foam pattern 20, which contacts the ingates 16 and 16 of the cores 12 and 12, is thicker than other parts of the lost foam pattern 20 and forms a feeder head. In case that the inverted triangle part 20 a is located on the parting lines of the cores 12 and that the cores and 12 are integrated, the inverted triangle part 20 a contacting the ingates 16 and 16 of the cores 12 and 12 may be a cast mold integrated with the cores 12 and 12 instead of the lost foam pattern.

Note that, the sprue cup 18 may be a shell mold or a self-hardening mold.

Further, lost foam patterns 22, which form discharging feeder heads, are respectively connected to communication holes, which are respectively opened in upper faces of the cores 12 and 12 and communicated to the cavities 14. The communication holes are formed on the parting lines of the cores 12 shown in FIGS. 1 and 2, but they may be formed in optional places, other than the parting lines, according to shapes of the cores 12. Note that, in case that the communication holes, which are communicated to the cavities 14 of the cores 12, are formed in the upper faces of the cores 12 and that the cores 12 and 12 are integrated, the discharging feeder heads may be formed by a cast mold integrated with the cores 12 and 12 instead of the lost foam patterns.

Outer faces of the lost foam patterns 20 and 22 are coated with a refractory mold coating agent, which is not molten or thermally decomposed by the molten metal poured into the sprue cup 18. Therefore, when the lost foam patterns 20 and 22 are thermally decomposed and disappeared by the molten metal poured into the sprue cup 18, the refractory mold coating agent forms outer faces of the sprue and the discharging feeder heads.

Note that, the inverted triangle part 20 a of the lost foam pattern 20 is connected to parts of the cores 12 and 12 including the ingates 16 and 16 by an adhesive.

In the casting unit shown in FIG. 1, the cores 12 and 12, the lost foam pattern 20 forming the sprue and the lost foam patterns 22 forming the discharging feeder heads are embedded in dry sand 24, except for the sprue cup 18 which is attached to an upper end of the lost foam pattern 20.

A tubular member 26, which has through-holes 26 a, 26 a, . . . , whose diameter is smaller than a grain diameter of the dry sand 24, is inserted in the dry sand 24. The tubular member is used to collect and discharge decomposition gasses, which are generated by contact between the cores 12 and 12, the lost foam patterns 20 and 22 and the molten metal.

Embedding the cores 12 and 12 and the lost foam patterns 20 and 22 in the dry sand 24 is performed by filling the flask 10, in which the cores 12 and 12 and the lost foam patterns 20 and 22 have been inserted, with a prescribed amount of the dry sand 24 and then applying vibration to the flask 10, or by filling the flask 10 with the dry sand with applying vibration thereto, so that gaps between the cores 12 and 12 and the lost foam patterns 20 and 22 can be filled with the dry sand 24.

By pouring the molten metal into the sprue cup 18 of the casting unit as shown in FIG. 1, the lost foam pattern 20 is thermally decomposed and disappeared, but the refractory mold coating agent, which has coated the outer faces of the lost foam pattern 20, forms a sprue 32 and prevents the molten metal from penetrating into the dry sand 24. A feeder head 32 a, which is thicker than the sprue 32, is formed, by the inverted triangle part 20 a, at a part of the sprue 32 near the cores 12 and 12.

The molten metal poured into the sprue 32 is introduced into the cavities 14 of the cores 12, via the ingates 16 of the cores 12 and 12 so as to fill the cavities. Further, the molten metal in the cavities 14 contacts the lost foam patterns 22 connected to the communication holes of the cavities 14, so that the lost foam patterns 22 are disappeared and the discharging feeder heads 34 are formed.

When the molten metal fills the cavities, resins of the lost foam patterns 20 and 22 and the cores 12 and 12 are thermally decomposed by the heat of the molten metal, and decomposition gasses are generated. The decomposition gasses are collected in the tubular member 26, via gaps between grains of the dry sand 24 and the through-holes 26 a, 26 a, . . . , and discharged to the outside from an outlet of the tubular member 26.

Note that, by providing an ignition unit, e.g., sparking plug, to the outlet of the tubular member 26, the decomposition gasses discharged from the tubular member 26 can be burned.

When the cavities 14 of the cores 12 and 12 are filled with the molten metal, pouring the molten metal into the sprue cup 18 is stopped, and then the molten metal in the cavities 14 is cooled.

While cooling the molten metal in the cavities 14, gaps will be formed in the cavities 14 by shrinkage of the molten metal being cooled. But, the gaps can be filled with the molten metal stored in the feeder head 32 a or the discharging feeder heads 34.

When cooling the molten metal in the cavities 14 is completed, a cast body, in which cast products P formed in the cavities 14 of the cores 12 and 12 and a cast runner 36 formed in the sprue 32 are integrated as shown in FIG. 3, is produced.

The cast body can be pulled out from the dry sand 24 after the dry sand 24 is plasticized by applying vibration.

In the cast body 30 shown in FIG. 4 which has been pulled out from the dry sand 24, the cast products P, which have been formed in the cores 12 and 12, are connected to a cast feeder head part 36 a (a part formed in the feeder head 32 a) by cast ingate parts 38 and 38 formed by the ingates 16 and 16.

By patting the cores 12 and 12 of the cast body 30, the cores 12 and 12 can be separated from the cast runner 36, and the cores 12 and 12 are simultaneously broken, so that the cast products P and P can be taken out.

Cast discharging feeder head parts 40 a and 40 a, which are formed in the discharging feeder heads 34, are projected from outer faces of the cast products P and P taken out from the cores 12 and 12. The cast discharging feeder head parts 40 a and 40 a can be easily cut and removed.

As described above, the cores 12 and 12 are integrated by the adhesive, and the cores 12 and 12 can be handled as one body, so that the casting unit shown in FIG. 1 can be easily assembled and post-treatment can be easily performed.

The cast products P and P have smooth surfaces, and invasion of parts of the lost foam patterns 20 and 22 or soot into the cast products can be prevented.

When the cores 12 and 12 are separated from the cast runner 36, even if the cores 12 and 12 are not broken, components of the cores 12 and 12 contact the molten metal, organic matters, e.g., adhesive, are thermally decomposed and adhesive strength is lowered, so that the cores 12 and 12 can be easily broken and the cast products P and P can be easily taken out.

In FIGS. 1-4, the two cores 12 and 12 are used, but number of the cores may be two or more, for example, six cores 12, 12, . . . may be used as shown in FIG. 5. In FIG. 5, the ingates 16 of the cores 12, 12, . . . are faced each other, and the cores 12, which are adjacent to each other, are connected to each other. Therefore, the six cores 12, 12, . . . can be handled as one body.

The inverted triangle part 20 a, which is formed at a core 12 side end of the lost foam pattern 20 forming the sprue, is formed for forming the feeder head and connected to the ingates 16 of the center cores 12 and 12 of the arranged cores 12, 12, . . . .

Further, lost foam patterns 20 b and 20 b are extended, from the part 20 a provided to the center cores 12 and 12, toward the adjacent cores 12, 12, . . . . The inverted triangle parts 20 a are formed at prescribed positions of the lost foam patterns 20 b and 20 b and respectively connected to the ingates 16 of the adjacent cores 12, 12, . . . .

By using the cores 12, 12, . . . and the lost foam patterns 20, 20 a and 20 b, the cast product 30, in which the six cores 12, 12, . . . , in which the cast products P are formed, are connected to the lower end of the cast runner 36, can be obtained.

In FIGS. 1-5, the adjacent cores 12, 12, . . . are connected to each other by an adhesive, but the core 12 shown in FIG. 6 may be employed. The core 12 shown in FIG. 6 is constituted by a pair of core molds 12 a and 12 b. Concave parts 50 and convex parts 52 are formed in outer faces of the core 12.

In case of using the cores 12, 12, . . . shown in FIG. 6, the convex parts 52 of the core 12 are fitted in the concave parts 50 of the adjacent core 12, i.e., concavo-convex engagement, so as to integrate the cores 12, 12, . . . and handle them as one body.

When the concave parts 50 of the core 12 and the convex parts 52 of the adjacent core 12 are concavo-convex-engaged, an adhesive may be applied to the engaged parts.

Further, as to the adjacent cores 12, 12, . . . shown in FIGS. 1-5, another manner of connecting the cores 12 will be explained.

In case of using the core 12 constituted by a pair of shell molds, the cores 12, which are adjacent to each other, can be connected to each other by tightly adhering their softened layers, in each of which a resin included in shell sand is softened, to each other.

A casting mold which is formed by a shell molding method with using the shell sand is generally called “shell mold”, and the shell sand is dry sand which is mixed with powders of the resin, e.g., phenol resin, hexamine. The shell sand is granulated at room temperature and softened by increasing temperature to the melting point of the resin. The softened shell sand is hardened by further increasing the temperature.

The core constituted by the pair of shell molds is produced by the steps of: applying vibration to the shell sand; pressing a pair of molds, which are heated, into the shell sand, which is being vibrated, from above; leaving the pair of molds in the shell sand for a prescribed period of time; lifting the shell molds, in each of which a hardened layer being hardened on a molding face and a softened layer, which covers the hardened layer and in which the resin included in the shell sand is softened, are formed, from the shell sand; and tightly adhering the softened layers to each other.

Details of the above described method of producing the shell molds will be explained with reference to the drawings.

As shown in FIG. 8, shell sand 85 is stored in a shell sand container 21. A vibrator 88, which applies vibration to the shell sand 85 in the shell sand container 21, is provided to the shell sand container 21. The vibrator 88 is, for example, a vibration motor.

By applying vibration to the shell sand 85 by the vibrator 88, frictional resistance between grains of the shell sand 85 can be reduced and the shell sand can be plasticized, so that a pair of molds 82 and 84 can be easily pressed into the shell sand 85 from above.

The molds 82 and 84 to be pressed into the shell sand 85 are located above the shell sand container 21, and their molding faces 51 and 54 are faced downward. Rear faces (opposite sides of the molding faces, i.e., upper faces) of the molds 82 and 84 are formed in concave portions 19, which are concaved toward the molding faces.

Chambers 86, which are isolated from the outside, are respectively formed in upper parts (rear side parts) of the molds 82 and 84 including the concave portions 19. Heating means, e.g., heaters 80, are respectively provided in the chambers 86. The heaters 80 are, for example, electric heaters and capable of heating air in the chambers 86.

Each of the chambers 86 is constituted by a frame 27, which is vertically extended from an upper part of the mold 82 or 84 and encloses the chamber 86, and a top plate 53, which covers an upper face of the frame 27. As to each of the chambers 86, the mold 82 or 84 constitutes a bottom part, the frame 27 constitutes side walls, and the top plate 53 constitutes a top part, namely the frame 27 and the top plate 53 are included in each of chamber constituting sections.

The molds 82 and 84 are respectively fixed to flanges 13, each of which is inwardly extended from the frame 27, by bolts, etc. The molds 82 and 84 may be composed of a material with high heat conductivity, e.g., aluminum. Aluminum is lighter than other metals, so the concave portions 19 composed of aluminum are capable of reducing their weights and can be easily handled.

Ejector pins 78, which eject completed shell molds A and B (see FIG. 15) from the molds 82 and 84, are provided in the chambers 86. Since the ejector pins 78 are provided in the chambers 86, they are heated as well as the molds 82 and 84.

Upper end parts of the ejector pins 78 pass through each of the top plates 53. The upper end parts of the ejector pins 78, which pass through the top plate 53, are fixed to each of the press plates 56. Lower end parts of the ejector pins 78 can be projected from and retracted into through-holes of each of the flanges 13. Lower end faces of the ejector pins 78 are usually level with bottom faces of each of the flanges 13.

Each of the press plates 56 is located above each of the top plates 53 and always biased upward, with respect to each of the top plates 53, by biasing means 59, e.g., springs.

Press cylinder units 58, which actuate the ejector pins 78, are respectively provided above the press plates 56. Each of the press cylinder units 58 is located above each of the press plates 56, fixed to each of cylinder frames 60, and each of rods 58 a is fixed to each of the press plates 56.

By actuating the press cylinder units 58, the rods 58 a move the press plates 56 downward against biasing force of the biasing means 59. Then, the ejector pins 78, which are fixed to the press plates 56, are moved downward and projected from the through-holes. The ejector pins 78, which are projected from the through-holes, eject the shell molds A and B (see FIG. 15) from the molds 82 and 84.

In the above described embodiment, inner spaces of the chambers 86 are heated by the heaters 80, so leakage of the heated air from the chambers 86, via the through-holes of the top plate 53 and the flanges 13 through which the ejector pins 78 pass, may be ignored.

Note that, in case of spraying overheated steam or heated air into the chambers 86, inner pressures of the chambers 86 are increased, so the through-holes of the top plate 53 and the flanges 13, through which the ejector pins 78 pass, must be tightly sealed so as to prevent the overheated steam or heated air from leakage. Preferably, in this case, the ejector pins 78 are enclosed by constituting members of the frames 27 or the molds 82 and 84 so as not to expose the ejector pins 78 in the chambers 86.

Each of the chamber constituting sections, which includes the molds 82 or 84, is attached to a robot arm 70 of each of articulated robots and capable of rotating in the vertical plane, moving in the horizontal plane and moving upward and downward.

Turning means 71, e.g., motor, is provided to each of the robot arms 70, and a rotary shaft of the turning means 71 is connected to each of the chamber constituting sections. By actuating each of the turning means 71, bottom faces of the shell molds formed on the molding faces of the molds 82 and 84 can be faced each other.

In each of the robot arms 70, turning means 72, whose rotary shaft is arranged perpendicular to the rotary shaft of the turning means 71, is provided on the upper side of turning means 71. Further, turning means 74, whose rotary shaft is arranged parallel to the rotary shaft of the turning means 71, is provided on the upper side of turning means 72.

By actuating the turning means 72, the molds 82 and 84 can be moved in the direction perpendicular to a paper surface of the drawing of FIG. 8. Therefore, the bottom faces of the shell molds can be connected in a state where the bottom faces are slightly shifted each other.

By actuating the turning means 71 and 74, the molds 82 and 84 can be moved in the vertical direction and horizontal direction.

Upper ends of the robot arms 70 are not shown, but tuning means (not shown), whose rotary shafts are arranged in a prescribed direction, are attached to the upper ends, so that the molds 82 and 84 can be moved upward and downward by actuating the turning means of the robot arms 70.

For example, motors or cylinder units may be used as the turning means 71, 72 and 74.

A manner of connecting the shell molds will be explained with reference to FIGS. 9-16. Note that, the structural members, other than the molds 82 and 84 and the shell sand container 21, are omitted in the drawings.

Firstly, in FIG. 9, air in the chambers 86 of the molds 82 and 84 are heated by the heaters 80 provided in the chambers 86 respectively. Temperatures of the chambers 86 are set at about 250-300° C.

The vibrator 88 is started to apply vibration to the shell sand 85 in the shell sand container 21 before the molds 82 and 84 are downwardly moved into the shell sand container 21.

As shown in FIG. 10, when the temperatures of the molds reach at about 250-300° C., the robot arms 70 moves the molds 82 and 84 downward. When the entire molding faces of the molds 82 and 84 are embedded in the shell sand 85, the up-and-down movement is stopped. When the up-and-down movement is stopped, the vibrator 88 is also stopped.

The heaters 80 maintains the temperatures of the chambers 86 at a prescribed temperature with measuring the current temperatures of the molds 82 and 84 by temperature sensors (not shown).

In FIG. 11, the shell sand around the molding faces of the molds 82 and 84 are heated, and the shell sand is cured or hardened along the molding faces. In this process, only the shell sand near the molds 82 and 84 are hardened and form hardened layers Aa and Ba, and softened layers Ab and Bb, in which resin is not cured or hardened, are formed around the hardened layers. After the elapse of a prescribed period of time, the robot arms 70 move the molds 82 and 84 upward.

As shown in FIG. 12, by moving the molds 82 and 84 upward, the shell molds A and B, in which the hardened layers Aa and Ba and the softened layers Ab and Bb are formed along the molding faces, are moved upward together with the molds 82 and 84. Note that, grains of the shell sand stick onto outer faces of the softened layers Ab and Bb moved upward together with the softened layers, but the grains of the shell sand fall into the shell sand container 21 while or after moving the molds upward. To remove the shell sand, vibrators may be provided to the chamber constituting sections respectively. By vibrating the chamber constituting sections by the vibrators, the molds 82 and 84 are vibrated and the disused shell sand sticking on the softened layers Ab and Bb can be easily removed therefrom.

In FIG. 12, the molds 82 and 84 are turned in the directions indicated by arrows, by actuating the turning means 71, etc. of the robot arms 70, until bottom faces of the shell molds A and B face each other.

In FIG. 13, the bottom faces of the shell molds A and B face each other. In this state, the softened layers Ab and Bb exist on the shell molds A and B.

In the state shown in FIG. 13 where the bottom faces of the shell molds A and B face each other, the robot arms 70 move the chamber constituting sections, in the directions indicated by arrows, close to each other.

In FIG. 14, the softened layers Ab and Bb of the shell molds A and B are tightly contacted each other, and the softened layers Ab and Bb are cured or hardened by the heat of the molds 82 and 84, so that the two shell molds A and B can be securely connected to each other without using an adhesive.

In FIG. 15, the shell molds A and B, whose bottom faces are connected, are burned. The softened layers Ab and Bb of the shell molds A and B are gradually cured or hardened by the heat of the molds 82 and 84. Further, the softened layers Ab and Bb may be heated, from outside, by burning units 35 so as to promote the hardening of the softened layers.

Finally, as shown in FIG. 16, the ejector pins 78 eject the shell molds A and B, which have been integrated, from the molds 82 and 84, which have been moved upward, so that the connected shell mold U, in which the bottom faces of the shell molds A and B are connected to each other, is completed.

The softened layers including the softened resin are tightly contacted each other in the process of producing the shell molds, so that the plurality of shell molds can be easily produced, by the above described connecting manner, in comparison with the manner in which the adjacent cores are connected by an adhesive or concavo-convex engagement. 

1. A casting unit, comprising: a plurality of cores having molten metal inlets, which open into the surfaces of the cores and through which a molten metal is caused to flow into cavities formed in the cores; and a lost foam pattern forming a sprue between each of the molten metal inlets and a sprue inlet, in which a molten metal is poured, the lost foam pattern having a peripheral surface coated with a refractory mold coating agent, wherein the cores and the lost foam pattern are embedded in dry sand except for the sprue inlet, the casting unit is characterized in that the cores, which are adjacent to each other, are connected to each other so that the plurality of cores are integrated.
 2. The casting unit according to claim 1, wherein the cores, which are adjacent to each other, are connected to each other by an adhesive or concavo-convex engagement.
 3. The casting unit according to claim 1, wherein each of the cores is constituted by a pair of core molds.
 4. The casting unit according to claim 1, wherein the cores are constituted by shell molds, self-hardening molds or combination of the both.
 5. The casting unit according to claim 4, wherein the cores are constituted by the shell molds, and wherein the cores, which are adjacent to each other, are connected to each other by bringing softened layers of the shell molds, in which resin included in the shell sand is softened, into tight contact with each other and hardening the softened layers.
 6. The casting unit according to claim 1, wherein inner wall faces of the cavities formed in the cores are coated with a refractory mold coating agent.
 7. The casting unit according to claim 1, wherein the cores, the sprue, the sprue inlet and the dry sand are inserted in a metal flask, and a tubular member having a plurality of through-holes, whose diameter is smaller than a grain diameter of the dry sand, is inserted in the dry sand so as to collect and discharge a decomposition gas, which is generated by contact between the cores, the lost foam pattern and the molten metal.
 8. A casting method being performed in the casting die of any one of claims 1-7, said method comprising the steps of: plasticizing the dry sand, by applying vibration, after pouring the molten metal into the sprue inlet; and pulling a cast body, in which runners, which are formed by filling the sprue formed by the lost foam pattern with the molten metal, and products, which are formed by filling the cavities of the cores with the molten metal, are integrated, out from the dry sand. 